Hydrofoil with features to generate cavitation

ABSTRACT

A hydrofoil includes a hydrofoil body that extends between a base and a tip, a leading end and a trailing end, and a suction side and a pressure side that define a thickness there between. The hydrofoil body includes a discontinuous slope on at least one of the suction side or the pressure side. The discontinuous slope extends in a span-wise direction between the base and the tip such that the discontinuous slope decreases the thickness of the hydrofoil body from the leading end to the trailing end.

BACKGROUND

This disclosure relates to hydrofoils. Hydrofoils are known and used in engines, pumps, turbines and the like to propel a vehicle, move a fluid, or extract work from a fluid. As fluid flows around the hydrofoil, the localized pressure of the fluid can decrease and cause cavitation near the surfaces of the hydrofoil.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates an example desalination system.

FIG. 2 illustrates an example turbopump machine.

FIG. 3 illustrates a cross-section of a hydrofoil.

FIG. 4 illustrates a cross-section of another example hydrofoil.

FIG. 5 illustrates an example turbine section of a turbopump machine.

FIG. 6 shows a plurality of hydrofoils and cavitation regions extending from the hydrofoils.

FIG. 7 illustrates another example turbine section.

FIG. 8 illustrates an example radial turbine section of a turbopump machine.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates selected portions of an example desalination system 20, which provides an example operating environment for a turbopump machine 22 and hydrofoil 46 that will be described in more detail below. It is to be understood that the desalination system 20 is only an exemplary end use environment and that other systems, such as but not limited to aircraft or aerospace systems and turbine engines, will also benefit from the disclosed turbopump machine 22 and hydrofoil 46.

In the illustrated example, the turbopump machine 22 includes a pump section 24 and a turbine section 26. The turbopump machine 22 is fluidly connected with a reverse osmosis device 28 of known construction, for the desalination of water.

In the illustrated example, feed water is received into the pump section 24, which pressurizes the feed water and moves the feed water to the reverse osmosis device 28. As an example, the reverse osmosis device 28 includes one or more membranes to separate the feed water into a low-salinity stream 30 and a saline stream 32. The saline stream 32 is fed into the turbine section 26 of the turbopump machine 22, for energy recovery.

FIG. 2 illustrates an example of the turbopump machine 22. The pump section 24 and the turbine section 26 are coupled with a rotatable shaft 40 for rotation about axis A. The pump section 24 includes an impeller 42 that is coupled to rotate with the rotatable shaft 40.

In this example, the turbine section 26 is an axial turbine that is coupled to drive the rotatable shaft 40. It is to be understood that the turbine section 26 can alternatively be a radial turbine. The turbine section 26 includes a rotor 44 having a plurality of hydrofoils 46 (one shown) that are used as rotatable blades. In this example, the turbine section 26 also includes a plurality of hydrofoils 48 that are used as static vanes. The hydrofoils 46 and 48 are in communication with an inlet 50 of the turbine section 26. An outlet 52 is located downstream from the hydrofoils 46. In the example shown, the outlet 52 is an annular outlet that extends between an outer wall 54 and an inner wall 56.

The design and operation of the hydrofoil 46 will now be described. It is to be understood, however, that the described features of the hydrofoil 46 are also applicable to the hydrofoil 48 that is used as a static vane. As illustrated in FIG. 3 and FIG. 5, each of the hydrofoils 46 includes a hydrofoil body 66 that extends between a base 68 and a tip 70, a leading end 72 and a trailing end 74, and a suction side 76 and a pressure side 78 that define a thickness 80 there between.

The hydrofoil body 66 also defines a mean camber line 82 that extends from the leading end 72 to the trailing end 74. The mean camber line 82 is the mid-thickness of the hydrofoil 46 such that, normal to the mean camber line 82, there is an equal amount of hydrofoil body distance above and below the mean camber line 82. Thus, the thickness 80 is taken normal to the mean camber line 82.

As shown in FIG. 3, the hydrofoil body 66 includes a discontinuous slope 84 on the suction side 76. The discontinuous slope 84 extends in a span-wise direction between the base 68 and the tip 70 such that the discontinuous slope 84 decreases the thickness 80 of the hydrofoil body 66 from the leading end 72 to the trailing end 74. That is, moving along the suction side 76 from the leading end 72 toward the trailing end 74, the discontinuous slope 84 causes a reduction in the thickness 80 of the blade body 66. It is to be understood that, although the discontinuous slope 84 is shown on the suction side 76, the discontinuous slope 84 can alternatively be located on the pressure side 78. In another alternative, the suction side 76 and the pressure side 78 each include a discontinuous slope 84.

In this example, the discontinuous slope 84 is closer to the trailing end 74 than to the leading end 72. For instance, the distance between the leading end 72 and the trailing end 74 is represented by a chord length and, relative to the chord length, the discontinuous slope 84 is closer to the trailing end 74.

In this example, the discontinuous slope 84 has an abrupt drop-off on the suction side 76. The abrupt discontinuity creates a face surface 86 that lies in or defines a plane that is transverse to the suction side 76. For instance, the face surface 86 is transverse to the suction side 76 on the leading end side and the trailing end side of the discontinuous slope 84. Thus, the face surface 86 defines a normal direction 88 that extends from the face surface 86 toward the trailing end 74 of the hydrofoil body 66.

The discontinuous slope 84 forms an included angle represented at 90 between the face surface 86 and the suction side 76 on the trailing end side of the discontinuous slope 84. In one example, the included angle is approximately 90 degrees.

FIG. 4 illustrates another example hydrofoil 146. In this disclosure, like reference numerals designate like elements where appropriate and reference numerals with the addition of one-hundred or multiples thereof designate modified elements. Corresponding elements are understood to incorporate the same features and benefits as each other. In this example, the hydrofoil 146 includes a discontinuous slope 184. The discontinuous slope 184 includes an apex 192 at which the slope of the suction side 76 changes. For instance, the apex 192 forms a distinct ridge along the span of the hydrofoil 146 such that the thickness of the hydrofoil 146 decreases across the apex 192 from the leading end side of the apex 192 to the trailing end side of the apex 192.

FIG. 5 illustrates an example of the turbine section 26 in operation. Although the hydrofoil 46 and discontinuous slope 84 are shown in this example, it is to be understood that the example is also representative of the hydrofoil 146 and discontinuous slope 184. In this example, the discontinuous slope 84 extends only partially between the base 68 and the tip 70, to generate a cavitation region (e.g., a vapor region) over less than the full span of the hydrofoil 46, as described below. Alternatively, as shown in FIG. 2, the discontinuous slope 84 extends entirely over the span of the hydrofoil 46 between the base 68 and the tip 70. That is, the span-wise size of the discontinuous slope 84 controls the height of the resulting cavitation region.

In operation, the turbine section 26 receives a fluid flow 200 through the inlet 50. The fluid flow 200 expands over the hydrofoils 46 to thereby drive the rotor 44 and, in turn, the pump section 24.

The discontinuous slope 84 of the hydrofoil 46 controls cavitation within the turbine section 26. In this example, the discontinuous slope 84 anchors a starting location of a cavitation region 202. As shown in FIG. 6, the cavitation region 202 extends from a leading side at the starting location S anchored at the discontinuous slope 84 to a trailing side at an ending location E that is downstream from the trailing ends 74 of the hydrofoil 46. That is, the discontinuous slope 84 of the hydrofoil 46 forces the cavitation to start at a specific location on the suction side 76 to thereby anchor the cavitation region 202. In this example, the starting location S at the discontinuous slope 84 is downstream of the intersection of plane P with the suction surface 76, where the plane P is normal to the suction side 76 and aligned with the tip of the trailing end 74. Upstream of the plane P is considered to be a covered portion of the suction side 76 and downstream is considered to be an uncovered portion with regard to the immediately adjacent hydrofoil 46.

Thus, when the cavitation region 202 collapses, it does so downstream from the hydrofoils 46 at a location that is also spaced from the walls 54 and 56 due to the partial extension of the discontinuous slope 84 between the base 68 and the tip 70 of the hydrofoil 46. The discontinuous slope 84 thereby provides the ability to control the location and collapse of the cavitation region 202 to avoid damaging the components of the turbine section 26. In comparison, a design that does not include the discontinuous slope 84 would experience random cavitation and collapse over the surfaces of the hydrofoils and end walls, which could cause damage to those surfaces. Moreover, to limit cavitation, a design that does not include the discontinuous slope 84 is operated within certain operating parameters that limit the ability of the turbine to extract work. The disclosed discontinuous slope 84 therefore also permits a wider operating regime to efficiently extract work in the turbine section 26.

As also shown in FIG. 5, the outlet 52 has an annular shape that increases in size as a function of distance from the hydrofoils 46. That is, the walls 54 and 56 diverge from the hydrofoils 46. The outlet 52 thereby serves as a diffuser to diffuse flow exiting from the hydrofoils 46, which increases downstream pressure and causes the cavitation region 202 to collapse at a desired location downstream from the hydrofoils 46.

FIG. 7 illustrates a modified turbine section 326 that is the same as the turbine section 26 shown in FIG. 5 but does not include the inner wall 56. In this example, the flow of fluid from the hydrofoils 46 swirls, as represented by flow lines F, and backflows toward the hydrofoils 46. The swirling backflow is radially inwards of the hydrofoils 46 and creates a virtual inner boundary for the cavitation region 202 that creates an adverse pressure gradient downstream from the hydrofoils 46 and results in the collapse of the cavitation region 202.

FIG. 8 shows selected portion of another embodiment turbine section 426. In this example, the turbine section 426 includes hydrofoils 446 that have discontinuous slopes 484, as described herein in the prior examples. The turbine section 426 generally receives water along directional axis A₁ and discharges the water along directional axis A₂ that is substantially perpendicular to axis A₁.

Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments.

The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims. 

1. A hydrofoil comprising: a hydrofoil body extending between a base and a tip, a leading end and a trailing end, and a suction side and a pressure side that define a thickness there between, the hydrofoil body including a discontinuous slope on at least one of the suction side or the pressure side, the discontinuous slope extending in a span-wise direction between the base and the tip such that the discontinuous slope decreases the thickness of the blade body from the leading end to the trailing end.
 2. The rotor blade as recited in claim 1, wherein an apex of the discontinuous slope is closer to the trailing end than to the leading end.
 3. The rotor blade as recited in claim 1, where the discontinuous slope has an included angle of approximately 90 degrees.
 4. The rotor blade as recited in claim 1, wherein the discontinuous slope extends from the base to the tip.
 5. The rotor blade as recited in claim 1, wherein the discontinuous slope includes a face surface that lies in a plane that is transverse to the one of the suction side or the pressure side on which the discontinuous slope is.
 6. The rotor blade as recited in claim 5, wherein a normal direction of the face surface extends toward the trailing end.
 7. The rotor blade as recited in claim 1, wherein the discontinuous slope includes an apex at which a slope of the suction side changes.
 8. A turbopump machine comprising: a rotatable shaft; a pump coupled to rotate with the rotatable shaft; a turbine coupled to drive the rotatable shaft, the turbine including a plurality of hydrofoils that each have a hydrofoil body extending between a base and a tip, a leading end and a trailing end, and a suction side and a pressure side that define a thickness there between, the hydrofoil body including a discontinuous slope on at least one of the suction side or the pressure side, the discontinuous slope extending in a span-wise direction between the base and the tip such that the discontinuous slope decreases the thickness of the blade body from the leading end to the trailing end.
 9. The turbopump machine as recited in claim 8, wherein the pump includes an impeller.
 10. The turbopump machine as recited in claim 8, including an annular outlet extending from the turbine between an outer wall and an inner wall.
 11. The turbopump machine as recited in claim 10, wherein the annular outlet increases in size as a function of distance from the turbine.
 12. The turbopump machine as recited in claim 8, including an outlet extending from the turbine, the outlet being bounded only by an outer wall.
 13. The turbopump machine as recited in claim 12, wherein the outlet increases in size as a function of distance from the turbine.
 14. The turbopump machine as recited in claim 8, wherein the discontinuous slope has an included angle of approximately 90 degrees.
 15. The turbopump machine as recited in claim 8, wherein the discontinuous slope includes a face surface that lies in a plane that is transverse to the one of the suction side or the pressure side on which the discontinuous slope is.
 16. The turbopump machine as recited in claim 8, wherein the discontinuous slope includes an apex at which a slope changes.
 17. The turbopump machine as recited in claim 8, wherein the discontinuous slope is adapted to generate supercavitation downstream from the plurality of hydrofoils while the turbopump machine is in steady state operation.
 18. A method of controlling cavitation for a hydrofoil having a hydrofoil body extending between a base and a tip, a leading end and a trailing end, and a suction side and a pressure side that define a thickness there between, the method comprising: anchoring a starting location of a cavitation region using a discontinuous slope on at least one of the suction side or the pressure side of the hydrofoil body, the discontinuous slope extending in a span-wise direction between the base and the tip such that the discontinuous slope decreases the thickness of the hydrofoil body from the leading end to the trailing end, the cavitation region extending downstream from the hydrofoil beyond the trailing end.
 19. The method as recited in claim 17, including generating the cavitation region over less than the full span of the hydrofoil body.
 20. The method as recited in claim 17, including generating a backflow of fluid downstream from the hydrofoil body and radially inwards of the hydrofoil body to provide an inner boundary of the cavitation region.
 21. The method as recited in claim 17, including diffusing flow downstream from the hydrofoil. 